1. Field of the Invention
The present invention deals broadly with the field of electrical interconnect systems, and more specifically to an electromechanical device which improves electrical continuity between a device under test (DUT), and a socket or contactor.
2. Description of the Prior Art
A plethora of applications exist for effecting electrical contact between two conductors. Once significant application is effecting interconnection between the leads of an integrated circuit device and conductive pads or terminals on a printed circuit board which serves to effect an interface between the integrated circuit (IC) device and a tester apparatus. Such apparatus are used to evaluate performance of integrated circuit devices.
Numerous considerations bear upon the contact structure employed to interconnect the IC and the printed circuit board. These factors include both electrical and mechanical considerations.
In practice, the design of contacts often render them more susceptible to environmental effects than most other components in an electronic system. Under certain operating conditions, corrosion (such as oxide build-up) can set in on the contact apparatus, causing changes in the contact resistance, resulting in intermittent failures on the contact. Such failures are difficult to detect visually, and can be of critical importance in high-speed digital electronics applications which must have uninterrupted operation to function properly.
One way in which designers of contact systems have dealt with the build up of oxides and other corrosive materials at contact points is through the introduction of a mechanical xe2x80x9cwiping actionxe2x80x9d between the contact itself and the lead of an integrated circuit by which the contact is engaged. The wiping action functions to effect maximization of effective contact in view of oxide build-up which can occur. In effect, the wiping action enables a good interface to be accomplished between the contact and the lead of the IC. Some examples of this concept of a mechanical wiping action can be found in the Contact of U.S. Pat. No. 4,445,735 issued to Bonnefoy on May 1, 1984 and the Contact of U.S. Pat. No. 5,207,584 issued to Johnson on May 4, 1993. Column 2, lines 62-68 and column 3, lines 1-2 of this invention provides: xe2x80x9cA rigid first element is received in the trough formed in the first surface and extends across any slots in which one or more contacts are received. An elastomeric second element is received in the trough formed in the second surface of the housing and extends across the one or more slots in which contacts are received. The elastomeric second element is provided with a measure of compressibility and tensile extendability.xe2x80x9d Further in column 3, lines 32-48: xe2x80x9cAs a particular lead of an integrated circuit device engages the protrusion of a corresponding contact and exerts downward pressure upon the protrusion, the channel in the contact will move relatively to the rigid first element received therein, and the contact will, effectively, be made to rotate to some extent as a result of the rigid first element moving, relative to the contact, more deeply into the channel formed in the contact. The downward force exerted by the lead of the integrated circuit upon the contact will have components along both X and Y axes, and these components will effect the apparent rotation of the contact. As a result, the protrusion will move laterally to some degree across the surface of the integrated circuit lead by which it is engaged, and the nub of the contact will move laterally across the integrated circuit board terminal with which it is in contact.xe2x80x9d
Another approach which has been undertaken to improve the electrical continuity performance of semiconductor test systems is the introduction of a low frequency/high amplitude ultrasonic transducer into an interconnect system. In such a system, the microscopic mechanical wiping action produced from a low frequency/high amplitude ultrasonic transducer serves to clean the contact site and reduces the site""s apparent contact resistance. One problem inherent to the low frequency/high amplitude approach is its low effective wiping action due to its extremely low frequency of operation.
The present invention overcomes many of the disadvantages associated with the prior art by providing a high performance electromechanical device which improves electrical continuity between a device under test (DUT) and a socket (or contactor), ideally suited for, but not necessarily limited to automated semiconductor test.
In this present invention, an ultrasonic transducer is incorporated into the test set-up such that its ultrasonic energy is coupled either into the DUT and thereby into the contacts of the socket or is coupled into the contacts of the socket and thereby into the leads (or equivalent I/O) of the DUT. It is the coupling of the ultrasonic energy between the leads (or other contact I/O) of the DUT and the contacts of the socket, for the purpose of enhancing electrical continuity, that comprises the present invention.
The present invention enhances electrical continuity by reducing apparent contact resistance and by reducing the apparent contact resistance force rate. These parameters are effectively reduced by virtue of a high frequency but small amplitude mechanical wiping action between the contacting surfaces, generated by said ultrasonic coupling. This high frequency/low amplitude mechanical wipe action can be varied and controlled to yield an effective wipe which is from 10 times to 100,000 times greater than the current state of the art (a low frequency/high amplitude approach).
The xe2x80x9cEffective Wipe Actionxe2x80x9d parameter shown in Table 1 above, typifies the difference between the current state of the art and the improvements incumbent to the present invention. Note that the value of the Effective Wipe Action parameter is referenced per second (of contact time). With such a great increase in the Effective Wipe Action parameter, one must be careful to limit contact force so that tribologic wear is not severely increased.
The present invention also allows the duration of the ultrasonic transducer""s xe2x80x9conxe2x80x9d time to be fixed and limited to some initial delay time. This time is sufficient to provide initial electrical continuity but allow testing of the DUT while the ultrasonic transducer is off. In another embodiment, the ultrasonic transducer""s xe2x80x9conxe2x80x9d time is variable and controlled so that initial electrical continuity between the DUT and the tester is monitored and controlled. A provision will be made to turn off the ultrasonic transducer at some (variable) time and fail the DUT for xe2x80x9ccontinuityxe2x80x9d.